AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Variation in Aerosol Nucleation and Growth in Coal-Fired Power-Plant Plumes due to Background Aerosol, Meteorology and Emissions: Sensitivity Analysis and Parameterization
ROBIN STEVENS, Jeffrey Pierce, Dalhousie University
Abstract Number: 69 Working Group: Aerosol Physics
Abstract New-particle formation in the plumes of coal-fired power plants and other anthropogenic sulfur sources may be an important source of particles in the atmosphere. It remains unclear, however, how best to reproduce this formation in global and regional aerosol models with grid-box lengths that are 10s of kilometers and larger. The predictive power of these models is thus limited by the resultant uncertainties in aerosol size distributions. In this presentation, we focus on sub-grid sulfate aerosol processes within coal-fired power-plant plumes: the sub-grid oxidation of SO$_2 with condensation of H$_2SO$_4 onto newly-formed and preexisting particles.
Based on the results of the System for Atmospheric Modelling (SAM), a Large-Eddy Simulation/Cloud-Resolving Model (LES/CRM) with online TwO Moment Aerosol Sectional (TOMAS) microphysics, we develop a computationally efficient, but physically based, parameterization that predicts the characteristics of aerosol formed within coal-fired power-plant plumes based on parameters commonly available in global and regional-scale models. Given large-scale mean meteorological parameters, emissions from the power plant, mean background condensation sink, and the distance from the source, the parameterization will predict the fraction of the emitted SO$_2 that is oxidized to H$_2SO$_4, the fraction of that H$_2SO$_4 that forms new particles instead of condensing onto preexisting particles, the median diameter of the newly-formed particles, and the number of newly-formed particles per kilogram SO$_2 emitted.
We perform a sensitivity analysis of these characteristics of the aerosol size distribution to the meteorological parameters, the condensation sink, and the emissions. In general, new-particle formation and growth is greatly reduced during polluted conditions due to the large preexisting aerosol surface area for H$_2SO$_4 condensation and particle coagulation. The new-particle formation and growth rates are also a strong function of the amount of sunlight and NO$_x since both control OH concentrations. Decreases in NO$_x emissions without simultaneous decreases in SO$_2 emissions increase new-particle formation and growth due to increased oxidation of SO$_2.
The parameterization described here should allow for more accurate predictions of aerosol size distributions and a greater confidence in the effects of aerosols in climate and health studies.